The present invention starts from a premix burner for a gas turbine in the form of a so-called “double-cone burner”, as is known, for example, from U.S. Pat. No. 5,921,770, which is incorporated by reference. The first figure of this application is generally reproduced here as FIG. 1.
The premix burner 10 according to FIG. 1 is comprised of two hollow partial cone shells 11, 12 which extend along an axis (29 in FIG. 2) and are nested one inside the other in an offset manner in relation to each other. The offset of the respective center axis or longitudinal symmetry axis of the partial cone shells 11, 12 in relation to each other creates, on both sides, in a mirror-image arrangement, a tangential air inlet duct 18, 19 in each case through which combustion air 20 flows into the conical inner space 30 of the burner. The two partial cone shells 11, 12 have in each case an entry section in the form of a cylinder 14, 15. Accommodated in the region of the cylinders 14, 15 is a nozzle 24 for atomizing a preferably liquid fuel 23 which, after combustion together with the injected combustion air 20, forms a flame front 28.
Naturally, the premix burner 10 can be of purely conical design, that is to say without the cylinders 14, 15. The partial cone shells 11, 12 furthermore have in each case a fuel line 16, 17 which are arranged along the tangential air inlet ducts 18, 19 and provided with injection openings 21 in the form of linear rows of holes through which a gaseous fuel 22 is injected into the combustion air 20 which flows past there, as is represented by means of arrows. These fuel lines 16, 17 are preferably placed at the latest at the end of the tangential inflow before entry into the inner space 30 in order to ensure optimum air/fuel mixing.
Towards the combustion chamber 25, the premix burner 10 has a front plate 13, serving as an anchor for the partial cone shells 11, 12, with a number of holes 26 through which cooling air 27 can be fed to the front section of the combustion chamber 25 as required.
The design and arrangement of the injection openings 21 for the gaseous fuel 22 has considerable influence upon the mixing of the fuel with the combustion air 20. The fuel 22 is injected into the air inlet passage 18, 19 of the premix burner 10 perpendicularly to the air flow. Mixing of the fuel 22 with the air is influenced both by the location of the injection openings 21 and by the flow velocity of the gaseous fuel.
In premix burners of the described type in use up to now, use is made of injection openings 21 which are represented as a row of holes R1 in FIG. 2, wherein such a row of holes is associated in each case with each of the two air inlet ducts 18, 19. If natural gas is used as the gaseous fuel, 32 injection openings 21 with a small outside diameter are arranged in the row of holes R1.
It has now transpired that during operation of such premix burners the mixing-through of the combustion air and the gaseous fuel can be improved more in order to lower the peak values of the flame temperature in the burner and therefore to reduce pollutant emissions (for example NOx).